Published papers

In immunoglobulin A nephropathy (IgAN), Cox regression analysis can select independent prognostic variables for renal functional decline (RFD). However, the correlation of the selected histological variables with clinical and/or treatment variables is unknown, thereby making histology-based treatment decisions unreliable. We prospectively followed 946 Japanese patients with IgAN for a median of 66 mo. and applied structural equation modeling (SEM) to identify direct and indirect effects of histological variables on RFD as a regression line of estimated glomerular filtration rate (eGFR) via clinical variables including amount of proteinuria, eGFR, mean arterial pressure (MAP) at biopsy, and treatment variables such as steroid therapy with/without tonsillectomy (ST) and renin-angiotensin system blocker (RASB). Multi-layered correlations between the variables and RFD were identified by multivariate linear regression analysis and the model's goodness of fit was confirmed. Only tubular atrophy/interstitial fibrosis (T) had an accelerative direct effect on RFD, while endocapillary hypercellularity and active crescent (C) had an attenuating indirect effect via ST. Segmental sclerosis (S) had an attenuating indirect effect via eGFR and mesangial hypercellularity (M) had accelerative indirect effect for RFD via proteinuria. Moreover, M and C had accelerative indirect effect via proteinuria, which can be controlled by ST. However, both T and S had additional indirect accelerative effects via eGFR or MAP at biopsy, which cannot be controlled by ST. SEM identified a systemic path links between histological variables and RFD via dependent clinical and/or treatment variables. These findings lead to clinically applicable novel methodologies that can contribute to predict treatment outcomes using the Oxford classifications.

An 88-year-old Japanese man with benign prostatic hyperplasia was presented to our hospital because of proteinuria and generalized edema. He was diagnosed with nephrotic syndrome and underwent a kidney biopsy, which revealed thickening of the capillary wall, spike formation, and subepithelial deposits, leading to histopathological diagnosis of membranous nephropathy. IgG4-dominant deposits were observed in IgG subclass staining, and immunostaining for thrombospondin type 1 domain-containing 7A (THSD7A) demonstrated granular staining along the capillary wall. A malignancy screening was performed, which led to the detection of gastric cancer. Malignancy-associated membranous nephropathy secondary to gastric cancer was suspected, and priority was given to the treatment of gastric cancer. Three months after undergoing radical surgery for gastric cancer, his nephrotic syndrome achieved remission. The histopathological diagnosis of gastric cancer was papillary adenocarcinoma. In the surgical specimen of the gastric cancer, THSD7A was positive in the tumor cells with intestinal phenotype and negative in gastric foveolar phenotype. These findings suggest that the acquisition of the ability to express THSD7A by cancer transformation in multi-step carcinogenesis of gastric cancer may be involved in the development of malignancy-associated membranous nephropathy.

Purpose: Deep learning (DL) is rapidly advancing in computational pathology, offering high diagnostic accuracy but often functioning as a “black box” with limited interpretability. This lack of transparency hinders its clinical adoption, emphasizing the need for quantitative explainable artificial intelligence (QXAI) methods. We propose a QXAI approach to objectively and quantitatively elucidate the reasoning behind DL model decisions in hepatocellular carcinoma (HCC) pathological image analysis. Approach: The proposed method utilizes clustering in the latent space of embeddings generated by a DL model to identify regions that contribute to the model’s discrimination. Each cluster is then quantitatively characterized by morphometric features obtained through nuclear segmentation using HoverNet and key feature selection with LightGBM. Statistical analysis is performed to assess the importance of selected features, ensuring an interpretable relationship between morphological characteristics and classification outcomes. This approach enables the quantitative interpretation of which regions and features are critical for the model’s decision-making, without sacrificing accuracy. Results: Experiments on pathology images of hematoxylin-and-eosin-stained HCC tissue sections showed that the proposed method effectively identified key discriminatory regions and features, such as nuclear size, chromatin density, and shape irregularity. The clustering-based analysis provided structured insights into morphological patterns influencing classification, with explanations evaluated as clinically relevant and interpretable by a pathologist. Conclusions: Our QXAI framework enhances the interpretability of DL-based pathology analysis by linking morphological features to classification decisions. This fosters trust in DL models and facilitates their clinical integration.

Mitochondrial diseases (MDs) are inherited metabolic disorders that affect multiple organ systems, including the kidneys. Variability in disease onset and phenotypic expression, combined with the absence of specific kidney pathological findings, pose significant challenges in diagnosing MD. Consequently, many undiagnosed cases of MD may exist among patients undergoing dialysis. No effective treatment for mitochondrial nephropathy has been established. We report the case of a 27-year-old female patient who presented with leg edema, nephrotic range proteinuria attributed to focal segmental glomerulosclerosis, and bilateral sensorineural hearing loss. Immunosuppressive therapy failed to achieve remission, resulting in progressive kidney function decline and eventual end-stage kidney disease. At hemodialysis initiation, worsening atypical cardiac function and hypertrophy prompted genetic testing, which identified an MT-TL1 m.3243 A > G mutation and confirmed the diagnosis of MD. After hemodialysis initiation, the patient experienced persistent fatigue and decreased physical activity levels despite dry weight management. Suspected stroke-like symptoms prompted the initiation of taurine supplementation, which significantly improved headache severity, cardiac function, and physical activity levels. This case highlights the therapeutic potential of taurine supplementation in patients with MD undergoing dialysis and the importance of maintaining clinical vigilance for MD across all stages of chronic kidney disease, even without characteristic renal pathological findings of mitochondrial nephropathy.

Tubulointerstitial nephritis (TIN) is a common kidney manifestation of Sjögren's syndrome, typically characterized by interstitial infiltration of T and B cells, with plasma cells being more prominent than in other etiologies. While most plasma cell infiltration in TIN is polytypic and the importance of the immunoglobulin isotypes expressed by the infiltrating plasma cells in the pathogenesis is unknown, recent reports have identified rare cases with monotypic IgA-positive plasma cell infiltration accompanied by monoclonal gammopathy of undetermined significance (MGUS). Here, we present three cases of Sjögren syndrome-associated TIN characterized by monotypic plasma cell infiltration. In all cases, the isotype of the infiltrating plasma cells was consistent with that of the predominant serum immunoglobulin. One patient exhibited IgA-type MGUS, one had IgM-type MGUS, and one showed elevated serum IgG levels along with IgG-positive plasma cell infiltration, but without detectable paraproteinemia. Notably, serum immunoglobulin levels decreased in parallel with improvement in kidney function. These findings suggest a potential link between the systemic immunoglobulin profile and local immunopathology of the kidneys in Sjögren's syndrome. Further case accumulation is needed to clarify the clinical significance and pathophysiology of monotypic plasma cell infiltration in TIN associated with Sjögren's syndrome.

Phospholipase A2 receptor (PLA2R) is the most common primary target antigen of idiopathic membranous nephropathy (MN) although PLA2R antibodies are also reported to be present in malignancy-associated MN. However, a case of PLA2R-positive MN secondary to PLA2R-positive carcinoma has not been reported. A 26-year-old Japanese woman presented with general fatigue, fever, and nonproductive cough. Computed tomography demonstrated a left kidney mass with pathologic diagnosis of Xp11.2 translocation renal cell carcinoma (RCC). After the second time of administration with Sunitinib, the patients exhibited significant proteinuria and hypoalbuminemia. Renal biopsy revealed a diagnosis of diffuse MN secondary to RCC. Immunofluorescence staining showed granular patterns positive for immunoglobulin (Ig) G, IgA, and C3c. PLA2R and IgG1-3 were positive, while IgG4 was negative. For the treatment of severe nephrotic syndrome, we attempted steroid therapy without any clinical improvement. Open nephrectomy was performed and surprisingly, RCC was stained for PLA2R with polarity for the basal side. At outpatient follow-up, 4 months after the operation, urinary protein had still persisted, although serum albumin was slightly increased. We report a case of PLA2R-positive MN secondary to PLA2R-positive RCC.

A 65-year-old man with valvular disorder presented to his physician because of widespread purpura in both lower extremities. Blood tests showed elevated serum creatinine levels and proteinase 3-anti-neutrophil cytoplasmic antibody (ANCA) with hematuria, suggesting ANCA-related rapidly progressive glomerulonephritis (RPGN). Although multiple blood cultures were negative, transthoracic echocardiography revealed warts in the valves, and a renal biopsy also showed findings of glomerular infiltration by mononuclear leukocytes and C3 deposition in the glomeruli, suggesting infection-related glomerulonephritis. Later, Bartonella antibody turned positive. Antimicrobial treatment improved the purpura and renal function without any recurrence. ANCA-positive RPGN requires the exclusion of infective endocarditis, especially that induced by Bartonella spp.

A 46-year-old woman developed takotsubo cardiomyopathy and nephrotic syndrome. The first kidney biopsy suggested non-immune-complex-mediated membranoproliferative glomerulonephritis (MPGN), and she was diagnosed with glomerular endothelial injury associated with takotsubo cardiomyopathy. A second biopsy was performed two years later because of persistent proteinuria despite renin-angiotensin system inhibition. This biopsy indicated non-immune-complex-mediated MPGN, but a mesangial and subendothelial substance of a higher electron density than that in the first biopsy was detected, suggesting the possibility of glomerular disease with non-immune deposits rather than endothelial injury. Finally, she was diagnosed with fibronectin nephropathy. Although rare, fibronectin glomerulopathy should be considered in non-immune-complex-mediated MPGN.

Fabry disease (FD) is an X-linked genetic lysosomal disorder caused by alpha-galactosidase A (GLA) deficiency. Multiple myeloma (MM) predominately affects older adults, which ranks as the second commonest hematological malignancy. Their overlap has rarely been reported. We present a case of the coexistence of FD and MM in a patient. We report the case of a 68-year-old woman who was referred to our hospital for the evaluation of thoracic spine tumor with bone destruction. On admission, her serum creatinine (Cr) level was elevated to 12.70 mg/dL from the baseline value of 0.91 mg/dL. Bone marrow aspiration revealed MM. Renal biopsy showed myeloma cast nephropathy, which was the primary cause of acute kidney injury. Renal pathology also showed podocyte swelling and tubule myeloid bodies in a mosaic pattern compatible with female FD. Consequently, the patient was diagnosed as FD based on the germ line mutation in GLA. The patient was treated with bortezomib and dexamethasone therapy, which significantly improved the renal function. This is the second case demonstrating a potential pathogenic relationship between FD and MM. Since FD is one of the few genetic diseases for which there are therapeutic agents with fewer side effects, diagnostic value of FD is high. If an MM patient has multiple organ abnormalities or any familial history, the physician should suspect FD.